The present invention relates to a device for measuring resistivity, and specifically to a device for non-invasively and non-destructively measuring the resistivity of a buried conductive layer.
Wrap assemblies used for shipping and storing electronic parts frequently contain a buried conductive layer to protect the electronic parts from electrostatic discharge. The buried layer, which is usually protected by an anti-static outer layer, acts as a Faraday cage to conduct harmful current around instead of through the wrap assembly. The lower the resistivity of the buried layer, i.e., the higher the conductivity, the more effective the buried layer is as a protection medium. It is therefore desirable to be able to test the resistivity of the buried layer.
While it is relatively simple to measure the resistivity of an exposed layer, measurement becomes more difficult when the layer is not directly exposed. Several existing measuring devices, which measure the resistivity of a buried layer by stripping away or puncturing the outer layer, are undesirable because they damage the outer layer. Because the outer layer serves a protective function, resistivity measurements should take place without damaging this layer.
Other existing measurement devices determine the resistivity of the buried layer by capacitively coupling to the buried layer with electrodes. However, these existing measuring devices must compensate for the impedance of the coupling capacitors. Such calculations involve complicated methods calling for expensive and computationally intense rf bridge techniques, which increase the cost of the measuring devices.